Heat sealing apparatus for closure of paperboard package flaps

ABSTRACT

Apparatus for heat-sealing paperboard package closure flaps having a heat sealable coating. While the package moves, two flaps are brought into proximity along two planes diverging at an acute angle, and upon the facing flap surfaces, are impinged one or more high-volume, low-velocity streams of very hot air, each along a controlled narrow area to heat one or more critical strips of each flap above the heat-sealing temperature.

Howe

[ 1 June 6, 1972 HEAT SEALING APPARATUS FOR CLOSURE OF PAPERBOARDPACKAGE FLAPS Inventor: William J. Howe, Los Altos, Calif. Assignee:Georgia-Pacliic Corporation, Portland,

Oreg.

Filed: June 2, 1970 Appl. No.: 54,079

Related US. Application Data Division of sei. No. 795,786, Feb. 3, I969,abandoned, which is'a continuation-in-part of Ser. No.

' 696,794, Jan. l0, I968, abandoned.

[56] References Cited UNITED STATES PATENTS 3,509,68l 5/1970 Sass ..53/375 X 3,340,777 9/ I967 l-littenberger et al. ..53/375 X 3,249,024 5/ l966 Shiu .93/36 Primary Examiner-C. L. Albritton Attorney-Owen,Wickersham & Erickson [57] ABSTRACT Apparatus for heat-sealingpaperboard package closure flaps having a heat scalable coating. Whilethe package moves, two flaps are brought into proximity along two planesdiverging at an acute angle, and upon the facing flap surfaces, are imp-'inged one or more high-volume, low-velocity streams of very U.S. Cl...219/243,53/375, 22l9/374, hot air each along a controlled narrow areato heat one or 19/375 more critical strips of each flap above theheat-sealing temlnt. CI. ..H05b 1/00 peramm Field of Search ..2l9/243,374, 375; 53/375,

53/387, 388 11 Claims, 16 Drawing Figures AMBIENT AIR 1 2 '57 AMBIENTAIR PATENTEDJUH 6 I972 SHEEI 2 OF 3 FlG 2 Q /O OOO R m o wmww J M m. f wM a O- Q m G F g FlG ll ATTORNEYS PATENTEnJun sum 3,668,369

sum 30F a Rik 76 mm 7 77 I l I02 FIG..14

INVENTOR. WILLIAM J. HOWE FlG 15 ATTORNEYS HEAT SEALING APPARATUS FORCLOSURE OF PAPERBOARD PACKAGE FLAPS This application is a division ofapplication Ser. No.

795,786, filed Feb. 3, 1969 (now abandoned in favor of streamlinecontinuation Ser. No. 101,126, filed Dec. 23, 1970), which was acontinuation-in-part of application Ser. No. 696,794, filed Jan. 10,1968 now abandoned. This invention relates to improvements in apparatusfor heat-sealing paperboard packages and the like. It relates to a novelheating apparatus and a novel manifold for emitting hot air against apair of package flaps that are to be scaled together.

Paperboard packages often have their flaps provided with heat-scalable(usually thermoplastic) coatings which are heated, and then the packageis closed and sealed by forcing the heated flaps together and holdingthem together until the heat scalable material is cooled sufficiently toprovide a tight seal. I-Ieretofore, there have been difficulties toaccomplishing this heat-sealing operation efiiciently without damagingthe carton or marring its outside surface coating, and, as a result,apparatus for accomplishing it automatically has tended to be veryexpensive. Also, whenpackaging frozen goods, it has often been difficultto employ heat sealing without damaging the goods themselves bysubjecting them to too much heat. Further, prior art apparatus is notreadily adjustable to changes in types of coatings or to speed changesin packaging machinery. A feature of the present invention is thatrelatively simple apparatus costing only about one-tenth orone-twentieth as muchas comparable prior-art apparatus can do the jobefficiently and well, without any damage to the frozen contentsinsi'clethe package or to the package itself, and can do so in a verysirnpleandfoolproof manner. Installation costs and maintenance costs are muchlower, too, and changes in coating types or in the speed of thepackaging machinery are readily made.

Some of the better prior-art systems have required special air driersfordrying the air before it is heated, because moist air damages theirheater elements, and they have required a supplemental air-compressorsystem in addition to the normal compressed air system of the packagingplant. The present invention operates without any special driers anduses normal plant' compressed air. No supplemental system is needed. Infact, my 'new system uses much less air than do the prior-art systems.-I

An important feature of the invention is the provision of a manifold andheater system in which heated air'at high temperature is evenlydistributed at low-velocity and high-volume over a relatively shortdistance to quickly heat the plastic coating on the flaps to thetemperature at which it becomes tacky or otherwise heat sealable. Thepresent invention does this in a single manifold without necessarilyhaving separate compartments in the manifold. An even flow of airthroughout the manifold is provided by spacing the discharge holes tobalance the naturally uneven input to those holes. At the holes, themanifold is independently positioned away from the flaps to enable flowof air. Also, by using separately controlled multiple heaters the system(with or without a partition in the manifold) can be used to provide adifferent temperature at one end or one portion of the manifold than atanother end or portion thereof for quick adaptability to various coatingtypes and machine speeds. I

The heater housings of the invention prewarm and predry ambient airwithout any supplemental warmers or driers being required, and theyprovide a swirl-type of air flow through the double jacket in the firsttwo of the three passes through the heater, thereby getting the greatestefficiency in air heating. Also, less heat is lost between the heatersdischarge into the manifold and the manifold discharge than is lost inconventional apparatus, partly because the outlet from the heaterelements is large and located quite close to the manifoldss dischargeopenings and partly because of the low velocity of the heated air, amajor feature of this system. As a result, the

device uses less wattage than conventional systems and wastes less heat.

In this invention no insulation of any kind is needed over or around theheater housings, yet their outer walls are actually barely warm to thetouch, although extremely hot air (typically 1,000 to 1,200" F) is sentfrom the heaters into the manifolds. It is the only system in use todaywithout insulation.

Another feature of the invention is that the air stream flow from themanifolds is designedto contact the flaps only where it is needed andnot over their full surfaces. The low velocity of the air stream helpshere. The flaps do not touch the manifold while they are being heated,and when they are being cooled, they do not require back-up pressure.

This invention employs much less air than conventional systems and usesit efiiciently at the flaps and at low velocity; so it does not inflatethe packages, as do many prior-art systems, and as a result, there is notime and space wasted in waiting for packages to deflate before packingthem in cases. Also, no temperature correction of the product isnecessary and there is no product deterioration.

To summarize theinvention briefly, the apparatus includes a hot airmanifold having two surfaces meeting at a sharp acute angle, each suchsurface having at least one row of openings along it for emitting theheated air. These openings are positioned away from the flaps, so thatthe air can move away. A novel air heater connected to the manifoldcomprises a long slim cylindrical ceramic heater with a plurality ofcircumferentially spaced long air passages, an inner shell surroundingand against the outer wall of the ceramic heater. Around the inner shelland spaced from it to provide a passage is an intermediate shell, and anouter housing surrounds the intermediate shell and is spaced from it toprovide a passage; this outer housing has a tangential air inlet. Hence,the air gets three passages through the heater. The ends of theintermediate shell and outer housing are closed, while the ceramicheater is connected directly to the manifold at one end and is s aced atits other end from the closed end of the intermediate shell. Theintermediate shell has aperture means at the end opposite the inlet, sothat air entering the tangential inlet is swirled between the outerhousing and the intermediate shell for its first passage, then goesthrough the aperture in the intermediate shell and is swirled around theinner shell in its second passage, goes through the heating passages inthe ceramic heater for its third passage, and then enters the manifoldthrough a large outlet. At the manifold the outlet holes are so spacedthat the air flow is longitudinally even, and thearea of the air flow isbalanced to the area of the inlet so that no excess pressure isgenerated by the expansion of heated air and so that the outlet holessupply the air at the same low velocity as that of the entering air.

Other objects and advantages of the invention will appear from thefollowing description of some preferred embodiments.

In the drawings:

FIG. 1 is a fragmentary top plan view of a package closure system ofthis invention, including a conveyor system along which paperboardcartons (which may contain frozen food or any other contents) are movedthrough the flap-heating and heat-sealing stages, which embody theprinciples of the invention.

FIG. 2 is an enlarged view in section taken along the line 22 in FIG. 1.

FIG. 3 is an enlarged view in section taken 33 in FIG. 1.

FIG. 4 is an enlarged view in side elevation taken line 44 in FIG. 1.

FIG. 5 is a view in section taken along the line 5-5 in FIG. 4.

FIG. 6 is a view of aportion of FIG. 5, shown with holding along the Irollers bearing against the outer major carton flaps to hold it closedagainst the inner major flap, during cooling and congealing of theheat-sealing coating.

FIG. 7 is an enlarged view in elevation and in section taken along theline 7-7 in FIG. 1 showingthe air heating of the coating on the outermajor and inner major flaps by a manifold of this invention.

along the line FIG. 8 is an enlarged view takenin section along the line88 in FIG. 1, showing closure of the heated flaps of FIG. 7.

FIG. 9 is a view taken along the line 9-9 in FIG. 2, showing thestructure of the air heater.

FIG. 10 is a view in perspective of a double manifold unit of theinvention, used for closure of wide flap systems with overlap.

FIG. 11 is a fragmentary view in section taken along the line 11-11 inFIG. 10.

FIG. 12 is a fragmentary view in section of a modified form of manifoldalso embodying the principles of the invention,

j'employing a somewhat different shape and two double rows of dischargeopenings.

FIG. 13 is a view similar to FIG. 5 of closing rollers for use with themanifold of FIG. 12.

FIG. 14 is a similar view of another form of closure device for bearingon four areas of the closure flaps.

FIG. 15 is a front elevational view of another modified form of manifoldhaving slots and flow-enabling recesses, with a portion cutaway to showthe rear wall.

. FIG. 16 is an enlarged fragmentary view in section taken I along theline'l6-16 in FIG. 15. As shown in FIG. 1, a paperboard carton 20 ismoved along a conveyor 21. The carton 20 has outer major flaps 22 and22a and inner major flaps 23 and 23a. These flaps 22, 22a and 23, 23aare to be closed against each other and sealed. At least one of theflaps 22 and 23 has been coated on one of the two facing surfaces 24 and25 (FIG. 7) with a suitable thermoplastic or other material enablingheat sealing. Often both flaps are so coated. For example only, a frozenfood product, such as a pie, may have been placed inside the carton 20,and the .operation is to be conducted without in any way overheatingthat frozen food product or marring the outer surface of the carton. Oneach side of the package, the closure is'to be accomplishedsimultaneously, in order to maintain alignment of the carton 20, so thatthere are duplicate apparatus, one on each side of the conveyor 21,comprising identical flap-heating units 26 and 27 and identicalflap-closing units 28 and 29.

A narrow plow 30 precedes each heating unit 26 and 27 and bends theinner major flap 23 up to perpendicular position at the end of thecarton 20, and a rod plow 31'then bends the outer major flap 22 over toa suitable acute angle, as shown in FIG. 7, as the carton 20 approachesthe heating unit 26 or 27.

The plows 30 and 31 immediately precede and continue alongside of amanifold 32 and are made so that they correctly position the flaps 22and 23 but are not themselves subject to heat build-up when no'carton isrunning through the machine; they stay cool while the machine runsempty. The manifold 32 is a very important element of each heating unit26, 27 of the invention, and each manifold 32 is provided with at leastone or more heaters; in the embodiment shown in the drawings there are apair of such heaters 33 and 34. The manifold 32 emits very hot (e.g.,l,000 to l,200 F.) air at high volume and at low velocity; this airheats the plastic coating of certain narrow areas on the flaps 22 and23'above the temperature where the coating becomes tacky, and then theouter major flap 22 is closed against the inner major flap 23 by aclosing roller 35 or a plow and is held closed against it under pressureby the closure system 28 or 29, while cool air is blown against thecarton 20 and flaps 22 and 23 from a cool-air manifold 36.

All these will be now discussed in more detail.

In the form of the invention shown in FIGS. 1-11 each hotair manifold 32is provided with two walls and 41 meeting at a vertex 42 of a sharpacute angle. This makes it possible to bring the flap 22 close to theflap 23 at the manifold 32. Each wall 40 and 41 is provided at suitablelocations with a row of discharge openings 43 and 44 at differentdistances from the vertex 42 and not opposite each other, to assurecorrect overlap of the heated areas in the flaps. As shown in FIGS. 2and 7, the heated air through the openings 43 and 44 is directed againstthe flaps 22 and 23, the inner major flap 23 being perpendicular to itsmain carton walls, while the outer major flap 22 is at an acute angle,as set by the plow 31 and held in position, as by a rod 37, theresistance of the flap 22 to folding keeps it against the rod 37 withoutany spacing member having to be between the flaps 22 and 23. Themanifold 32 may be generally triangular in cross section, as shown inFIGS. 2 and 7, with a third generally vertical wall 45 provided with oneor more openings 46 and 47 to receive the output from the heater units33 and 34; in this instance two heater units 33 and 34 are shown, butthere may be only one heater or there may be more than two. Thelength ofthe manifold 32 depends partly on. the number of heaters and partly onthe speed of the conveyor. For packaging closure it may be about 3 to 8inches long, typically, but may be longer; for providing a manufacturersjoint at very high speeds, it may be a couple of feet long, e.g., 16 to48 inches long for a speed of 1,200 feet per minute.

As shown in FIG. 3, the openings 43 leading from the manifold 32 arespaced apart, not evenly but in a pattern which gives an evendistribution of the discharge air, and the openings 44 are similarlyspaced, so that the container flaps 22 and 23 are properly heated withina'very short travel, a few inches travel only. As shown in FIG. 7, themanifold walls 40 and 41 are spaced from and lie at an angle to the flapsurfaces 24 and 25 which they are to heat, thereby spacing the manifoldfrom the flap surface 25 in the vicinity of the openings 44, to enableflow of air, and only a small area 48, 49 of each flap surface 24, 25 isheated. The total area of the openings 43 and 44 is made sufiicient togive high-volume, low-velocity air flow, so that the hot air impingesagainst the flap surfaces 43, 44 to heat them without causing highvelocity in toward the vertex 42 and sending air. into the inside of thepackage being closed. Also, the openings 43 and 44 are not spaced thesame distance from the vertex 42 but are instead spaced toimpinge withflaps at areas '48 and 49 that lie at the same distance from where theflaps 23 and '24 meet; this means that the openings 43 lie closer to thevertex 42 than do the openings 44, and it means that very narrow areas48 and 49 can be heated and the heat confined to them, since they willmate accurately.

As shown especiailyin FIGS. 2, 3, and 9, each heater unit 33 or 34comprises an outer metal housing 50, an intermediate" metal shell 51,and a ceramic heater 52 with a close-fitting metal inner shell 53 aroundthe outer circumference of the heater 52. The housing 50, intermediateshell 51, and inner shell 52 are all cylindrical tubes and are radiallyspaced from each other to provide cylindrical annular passages 54 and 55on each side of the intermediate shell 51. The outer housing 50 isprovided with an inlet 56 leading generally tangentially into itadjacent the end distance from the manifold 32, to induce swirling ofthe air around the intermediate shell 51. A suitable air supply tube 57supplies ambient air under low pressure to the inlet 56. A pair of endclosure members 58, and 59 connect the outer housing 50 to theintermediate shell 51, the member 58 closer to the manifold 32 beingalso used to provide spacing, not only between the intermediate shell 51and housing 50 but also between the intermediate shell 51 and the innershell 52 and also a connection fitting 60 to the manifold opening 46 or47. The intermediate shell 51 is thus fully supported at both ends, tomaintain accurate spacing and prevent movement during operation, and itis provided with an outer and closure member 61 through which may extendan electrical power line 62 for the heater 53. The ceramic member 53 andits outer sheath, the shell 52, is held and spaced away from theintermediate shell 51 by the member 58 and by spacing and supportingscrews 63. Thus, there is an outer swirl passage 54 between the housing50 and the shell 51, an inner swirl passage 55 between the shell 51 andthe shell 52, and there is a plurality of straight-flow passages 64,each containing a helical heater element 65, running through the ceramicheater 53. The heating elements 65 extend the length of the ceramic body53, and provide intense air heating for the air passing through thepassages 64, which are the only airflow passages through the heater 53.What appears to be a cylindrical passage 66 is blocked intentionally andmerely serves to lessen the amount of ceramic body.

with resultant forcing of the air to retain the flaps in their closedAsa result of this structure, air enters tangentially through the inlet56 and swirls around in the first passage 54, going toward the manifold32. Near the end wall 58 closest to the manifold 32 it passes through aslot or other aperture or apertures 67 in the shell 51 and then swirlsback inside the second passage 55 to the opposite end 61 most distancefrom the manifold 32. Then it turns in and goes by the space 68 inthrough the plurality of third passages 64 and from there directly intothe manifold 32 through the opening 47, which is the full size of theheater 53, so that there is no restriction between the heater 53 and themanifold 32 but rather an enlargement there. In the manifold 32 it goesup and goes out the two series of discharge openings 43 and 44 impingingupon the thermoplastic coated flaps 22 and 23 as shown in FIG. 7. Theaccumulated total of the areas of the openings 43 and 44 in the manifold32 is about 1 percent of the accumulated open cross-sectional area ofthe passages 64 through the heater 53. This enables a rise in ambientair temperature to about 1,000 to 1,150 F. to take place withoutincreasing the velocity of the heated air. The purpose is to send avolume of hot air at low velocity through the openings 43 and 44 andagainst the areas 48 and 49, rather than to send high-velocity airthrough them unwanted places and and unwanted rapidity in the cooling ofthe air. The velocity of the air issuing from the openings 43 and 44 isactually lower than that going into the inlet 56. It has been found thatthis system heats the flaps 22 and 23 quite rapidly to a temperatureenabling their closing. Therefore, such a manifold 32 need only be a fewinches long. Most of the housing 50 is merely warm to the touch, thoughthe air inside is rapidly dried and heated and may emerge from theheater 33, 34 at temperatures up to l ,000l ,200 F., for example. 7

Right beyond the end of the manifold 32 are the closing rollers, whichpreferably comprise a pair of hemispherical rollers 70 and 71 contactingthe opposite faces of the carton 20, as shown in FIGS. 4 and 8, and thehemispherical roller 35, which engages the outer major flap 22 andcloses it against the inner major flap 23. While the hemispherical shapeis preferred, it is not essential in all cases. The low-friction roller35 is mounted with its fiat portion 72 parallel to the main walls of thecarton and perpendicular to the flap 23. The other rollers 70 and 71 aremounted perpendicular to this roller 35 and engage the walls 73 and 74of the carton 20, retaining the cartons shape and squareness while theflap 22 is pushed against the flap 23; these rollers 70 and 71 serve noother purpose than the prevention of distortion of the carton fromfriction of the closing roller 35; they, thus, insure that the edge ofthe flap 22 seals parallel to the score line of the flap 23.

Just beyond the closing rollers 35, 70, 71 are the hold-down rollersystems 28 and 29, each of which in the illustrated embodiment comprisestwo staggered rows of cylindrical rollers 75 and 76 and mounted to befree running and to engage the carton 20 as the carton 20 is moved alongthem by the conveyor 21. They provide sufficient pressure for retainingthe closure without putting so much pressure that it becomes difficultto move the carton 20. They do not seal the carton; they position whilethey cool and seal themselves. These rollers 75 and 76 are adjustablymounted, as shown in FIG. 5, between a lower plate 77, which holds theshaft 78 for the lower roller 76, and an upper manifold 36 which holdsthe shaft 79 for the upper roller 75, the plate 77, the manifold 36 andplate 77 being held together by a bolt 80 and spaced apart by a spacer81 which may be changed to give different spacing. The manifold 36 hasan inlet 82 for a supply of cold air, which can be simply ambientatmospheric air, and is provided with a series of discharge openings 83in a face 84, which are made to. point down against the carton 20 atapproximately the level where the horizontal faces meet the convex facesof the roller 70 and 71. By this means, the carton flaps 22 and 23 arerapidly cooled, and in only about 2 feet the carton can be released fromthe rollers 75 and 76, and it will remain tightly closed without anyadditional pressure being necessary.

As shown in FIGS. 10 and 11, the system may be applied as well to asystem having two outer flaps which overlap by using a staggered pair ofmanifolds 32 and 32a each with their heaters. First one outer flap issealed and then the other.

FIG. 12 shows a modified form of manifold with a rhom boidal shape,having a vertical wall 91 meeting an inclined upper wall 92, a rearvertical wall 93 and a lower inclined wall 94. This shape is oftendesirable, and for purposes of example is shown with two rows ofdischarge openings on each of the two upper walls openings 95 and 96 inthe wall 91 and openings 97 and 98 in the wall 92. There could, ofcourse, be single matched rows of openings or more than two rows perwall. The rows are, of course, matched to cause the impinged surfaces tomeet when the flaps are closed. Two rows of openings enable more sealingarea and sealing strength than does one row. Double rows are notgenerally practical with the manifold 32, for the divergency betweenrows would render the two rows different in the temperatures theyimpart. The rhomboidal shape does enable this, and positive spacing maybe obtained by rods 99 and 37, that enable air flow, which are notmounted on the manifold but beside it, to enable free adjustmentrelative to the manifold.

With double rows of discharge openings, as in FIG. 12, the holdingassemblies 28 and 29 are preferably modified as shown in FIG. 13 toreplace the bolt 80 and spacer 81 with a longer bolt 100 and a largespacer 101.

With even wider flaps and more rows of sealing plastic, the structure ofFIG. 14 may be used, with a bolt 102 and a bar 103 inserted between twospacers 104 and 105 and supporting on shafts additional rollers 106 and107. Many other modifications are possible.

The manifold may be varied in many ways. A manifold 110 is shown inFIGS. 15 and 16. It may have the rhomboidal shape of the manifold 90 buthas vertical slits 111 instead of double rows of openings to heat a wideband on the flaps. This wider hot-air path gives a broader seal that isfeasible with drilled holes. By way of illustration, there are alsoshown two recesses or slots 112 and 1 13 that intersect the slits 111.With these, themanifold 110 can be quite close to the flaps to be heatedeven touching them and still the slots 112 and 113 let the hot air flowfreely in a direction which prevents heating of undesired flap areas.Horizontal slots may be used in staggered formations, and various otheropening patterns may be used. A single heater may be attached to thesingle fitting 114 of the manifold 110.

To those skilled in the art to which this invention relates, manychanges in constmction and widely differing embodiments and applicationsof the invention will suggest themselves without departing from thespirit and scope of the invention. The disclosures and the descriptionherein are purely illustrative and are not intended to be in any senselimiting.

I claim:

1. In heat sealing apparatus for closure of paperboard package flapshaving heat-scalable coatings, a hot air manifold having two surfacesmeeting and terminating at a sharp acute angle, each surface having arow of openings therealong for sending hot air against two flap surfacesfacing and on opposite sides of said manifold, and air-heating means forsupplying said manifold with heated air, the total area of said manifoldopenings being large enough relative to said air-heating means so thatthe heated air issues from said manifold openings at lower velocity thanthat at which it passes through said air-heating means, so that lowvelocity air issues in large volume from said openings.

2. In heat sealing apparatus for closure of paperboard package flapshaving heat-scalable coatings, a hot air manifold having two' surfacesmeeting and terminating at a sharp acute angle, each surface having arow of openings therealong for sending hot air against two flap surfacesfacing and on op posite sides of said manifold, and air-heating meansfor supheated air, said manifold openings in said rows being spacedapart from each other at varying distances so that, having substantiallyidentical areas, all

openings, regardless of their proximity to said air-heating means, sendout substantially the same flow of heated air.

3. In heat sealing apparatus for closure of paperboard package flapshaving heat-scalable coatings, a hot air manifold having two surfacesmeeting and terminating at a sharp acute angle, each surface having arow of openings therealong for sending hot air against'two flap surfacesfacing and on opposite sides of said manifold, the row of one saidsurface lying at a difi 'erent distance from the vertex of said sharpacute angle than the row on the other said surface but at the samedistance relative to the flaps they are heating, so that they gentlyheat narrow strips on said flaps that coincide when the flaps are urgedtogether, and air-heating means for supplying said manifold with heatedair.

4. In heat sealing apparatus for closure of paperboard package flapshaving heat-scalable coatings, a hot air manifold having two surfacesmeeting and terminating at a sharp acute angle, said manifold having ashape that is generally triangular in cross section, with a verticalrear wall connecting the walls providing said two surfaces, and eachsaid surface having a row of openings therealong for sending hot airagainst two flap surfaces facing and on opposite sides of said manifold,and airheating means for supplying said manifold with heated air theretogenerally horizontally to said vertical rear wall.

5. in heat sealing apparatus for closure of paperboard package flapshaving heat-scalable coatings, a hot air manifold having two surfacesmeeting and terminating at a sharp acute angle, said manifold having ashape that is generally rhomboidal, with a vertical rear wall, avertical front wall providing one of said two surfaces and the otherwalls being inclined, each of said two surfaces having a row of openingstherealong for sending hot air against two flap surfaces facing and onopposite sides of said manifold and air-heating means lying generallyhorizontally and leading into said rear wall for supplying said manifoldwith heated air.

6. Heat-sealing apparatus for closure of paperboard package flaps havingheat-scalable coatings, including in combination:

a hot air manifold having two surfaces meeting and terminating at asharp acute angle, each surface having at least one row of openingstherealong for sending hot air against two flap surfaces facing and onopposite sides of said manifold, and

at least one air heater connected to said manifold for supplying hot airthereto, each heater comprising an outer.

metal tubular housing having first and second closed ends and atangential air inlet near said first closed end, an intermediate tubularmetal shell inside and spaced from said outer housing except at saidclosed ends and having near said second closed end radial aperturemeans, said intermediate shell being closed and fully supported at bothits ends, and a ceramic heater body having a surrounding shell on itsouter surface lying inside and spaced from said intermediate shell, saidceramic heater body having a plurality of lengthwise passages each witha heating element inside said passages leading through an enlargedoutlet through said housing, larger in cross-section than the totalcross-sectional area of said lengthwise passages, into said manifold atone end and said'body stopping short of said first closed end of saidintermediate shell at the other end, whereby air enters said tangentialinlet, swirls around in a passage between said housing and saidintermediate shell, flows through said aperture means, swirls towardsaid second closed end in a closedend passage between said intermediateand surrounding shells and then flows back through said lengthwisepassages into said manifold at high volume and relatively low velocity,the total area of said manifold openings being greater than the totalcross-sectional area of said lengthwise passages through said body, sothat air issues from said manifold openings at low velocity and gently,though in great volume.

7. The heat-sealing apparatus of claim 6 wherein said manifold openingsare substantially identical in size and are spaced apart at varyingdistances to secure substantially the same flow rate through each.

8. The apparatus of claim 8 wherein said manifold is unpartitioned andhas a plurality of spaced heaters spaced apart said manifold anddistribution of the heated air therealong.

9. The apparatus of claim 8 wherein said manifold openings aresubstantially identical in size and are spaced apart at vary ingdistances depending on the location of the outlets from said heatersinto said manifolds, such that, regardless of the proximity of theopenings to the heater, the flow is substantially identical.

10. An air heater for heat sealing apparatus having a manifold to whichsaid heater supplies hot air, said heater comprising I an outer metaltubular housing having first and second closed ends and a tangential airinlet near said first closed end,

an intermediate tubular metal shell inside and spaced from said outerhousing except at said closed ends and having near said second closedend radial aperture means, said intermediate shell being closed at bothits ends and positively supported at both its ends to assure accurateradial positioning along its full length,

40 a ceramic heater body having a surrounding shell on its outer surfacelying inside and spaced from said intermediate shell, said body having aplurality of lengthwise passages, each with a heating element inside,said passages leading through an enlarged outlet of said housing intosaid manifold at one end and said body stopping short of the closed endof said intermediate shell at said first closed end of said housing,said outlet being larger than the cross-sectional width of said passagesthrough said body, to prevent an increase in velocity of air passingthrough said outlet, 7

whereby air enters said tangential inlet, swirls around in a passagebetween said housing and said intermediate shell, flows through saidaperture means, swirls toward said second closed end in a closed endpassage between said intermediate and surrounding shells and then flowsback through said lengthwise passages and into said manifold atrelatively low velocity.

11. The air heater of claim 10 wherein said outer tubular housing, saidintermediate shell and said heater body are 0 detachable from each otherand from a said manifold.

from each other to provide a desired flow rate of heated air for.

UNITED STATES PATENT ()FFICE QETTFTCATE F CGRECTTUN Patent No. 3,668,369Dated June 6, 1972' I Inventor(s) William J. HGWe It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

T- Column 1; line 19, "to" should read -in--. Column 5, 7 line 18,"l,OOO" should read --l,O00F.--. Column 8, line 18, which is line 1 ofclaim 8, 'claim 8" should read --claim 7-",

Signed and sealed this 11 th day of November 1972.

l as AL) Attast:

EDWARD MQFLETCHER JR 6 ROBERT GOTTSCI-LALK attesting OfficerCommissioner of Patents PO-1050 UNITED STATES PATENT OFF ICE 6CERTIFICATE OF CORRECTIUN Patent No. 3,668,369 Dated June 6, 1972'Inventor(s) William J. Howe It is certified that error appears inv theabove-identified pater 1t and that said Letters Patent are herebycorrected as shown below:

1- Column 1, line 19, "to" should read --in--. Column 5, "1

line 18, "1,000" should read --l,OOOF.--. Column 8, line 18, which isline 1 of claim 8, "claim 8" should. read --claim 7----s Signed andsealed this lhth day of November 1972.

EAL) Att-est:

EDWARD PLFLETCHERJR. BUBEJRT GDTTSCEALK ltte sting Officer Commissionerof Patents

1. In heat sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, each surface having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, and air-heating means for supplying said manifold with heated air, the total area of said manifold openings being large enough relative to said air-heating means so that the heated air issues from said manifold openings at lower velocity than that at which it passes through said air-heating means, so that low velocity air issues in large volume from said openings.
 2. In heat sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, each surface having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, and air-heating means for supplying said manifold with heated air, said manifold openings in said rows being spaced apart from each other at varying distances so that, having substantially identical areas, all openings, regardless of their proximity to said air-heating means, send out substantially the same flow of heated air.
 3. In heat sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, each surface having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, the row of one said surface lying at a different distance from the vertex of said sharp acute angle than the row on the other said surface but at the same distance relative to the flaps they are heating, so that they gently heat narrow strips on said flaps that coincide when the flaps are urged together, and air-heating means for supplying said manifold with heated air.
 4. In heat sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, said manifold having a shape that is generally triangular in cross section, with a vertical rear wall connecting the walls providing said two surFaces, and each said surface having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, and air-heating means for supplying said manifold with heated air thereto generally horizontally to said vertical rear wall.
 5. In heat sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, said manifold having a shape that is generally rhomboidal, with a vertical rear wall, a vertical front wall providing one of said two surfaces and the other walls being inclined, each of said two surfaces having a row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold and air-heating means lying generally horizontally and leading into said rear wall for supplying said manifold with heated air.
 6. Heat-sealing apparatus for closure of paperboard package flaps having heat-sealable coatings, including in combination: a hot air manifold having two surfaces meeting and terminating at a sharp acute angle, each surface having at least one row of openings therealong for sending hot air against two flap surfaces facing and on opposite sides of said manifold, and at least one air heater connected to said manifold for supplying hot air thereto, each heater comprising an outer metal tubular housing having first and second closed ends and a tangential air inlet near said first closed end, an intermediate tubular metal shell inside and spaced from said outer housing except at said closed ends and having near said second closed end radial aperture means, said intermediate shell being closed and fully supported at both its ends, and a ceramic heater body having a surrounding shell on its outer surface lying inside and spaced from said intermediate shell, said ceramic heater body having a plurality of lengthwise passages each with a heating element inside said passages leading through an enlarged outlet through said housing, larger in cross-section than the total cross-sectional area of said lengthwise passages, into said manifold at one end and said body stopping short of said first closed end of said intermediate shell at the other end, whereby air enters said tangential inlet, swirls around in a passage between said housing and said intermediate shell, flows through said aperture means, swirls toward said second closed end in a closed-end passage between said intermediate and surrounding shells and then flows back through said lengthwise passages into said manifold at high volume and relatively low velocity, the total area of said manifold openings being greater than the total cross-sectional area of said lengthwise passages through said body, so that air issues from said manifold openings at low velocity and gently, though in great volume.
 7. The heat-sealing apparatus of claim 6 wherein said manifold openings are substantially identical in size and are spaced apart at varying distances to secure substantially the same flow rate through each.
 8. The apparatus of claim 8 wherein said manifold is unpartitioned and has a plurality of spaced heaters spaced apart from each other to provide a desired flow rate of heated air for said manifold and distribution of the heated air therealong.
 9. The apparatus of claim 8 wherein said manifold openings are substantially identical in size and are spaced apart at varying distances depending on the location of the outlets from said heaters into said manifolds, such that, regardless of the proximity of the openings to the heater, the flow is substantially identical.
 10. An air heater for heat sealing apparatus having a manifold to which said heater supplies hot air, said heater comprising an outer metal tubular housing having first and second closed ends and a tangential air inlet near said first closed end, an intermediate tubular metal shell inside and spaced from said outer housIng except at said closed ends and having near said second closed end radial aperture means, said intermediate shell being closed at both its ends and positively supported at both its ends to assure accurate radial positioning along its full length, a ceramic heater body having a surrounding shell on its outer surface lying inside and spaced from said intermediate shell, said body having a plurality of lengthwise passages, each with a heating element inside, said passages leading through an enlarged outlet of said housing into said manifold at one end and said body stopping short of the closed end of said intermediate shell at said first closed end of said housing, said outlet being larger than the cross-sectional width of said passages through said body, to prevent an increase in velocity of air passing through said outlet, whereby air enters said tangential inlet, swirls around in a passage between said housing and said intermediate shell, flows through said aperture means, swirls toward said second closed end in a closed end passage between said intermediate and surrounding shells and then flows back through said lengthwise passages and into said manifold at relatively low velocity.
 11. The air heater of claim 10 wherein said outer tubular housing, said intermediate shell and said heater body are detachable from each other and from a said manifold. 